1. Field of the Invention
The present invention relates in general to automotive seat slide devices, and more particularly to automotive seat slide devices of a type which is equipped with reinforcing means for assuring or keeping a locked connection between fixed and movable rails upon a vehicle collision or the like.
2. Description of the Prior Art
In automotive seat slide devices, there is a type which comprises two, viz., right and left rail units each including a fixed rail which is secured to a vehicle floor and a movable rail which is slidably engaged with the fixed rail and carries thereon a seat. At least one of the two rail units is equipped with a position lock mechanism for locking the movable rail at a desired fore-and-aft position relative to the fixed rail.
In order to clarify the task of the present invention, one conventional automotive seat slide device of the above-mentioned type will be described with reference to FIGS. 14 to 17 of the accompanying drawings. The conventional seat slide device shown in the drawings is disclosed in Japanese Utility Model First Provisional Publication 3-53331.
Referring to FIG. 15, there is shown one (viz., right one) of two rail units of the known seat slide device.
As shown in the drawing, the rail unit 1 comprises a fixed rail 3 which is secured to a floor of a motor vehicle, a movable rail 4 which is slidably engaged with the fixed rail 3 and a position lock mechanism 5 which can lock the movable rail 4 at a desired fore-and-aft position relative to the fixed rail 3.
The fixed rail 3 has a generally U-shaped cross section and has an axially extending slit 2 defined between two inward upper flanges 8a and 8b. One of side walls of the fixed rail 3 is formed with a plurality of aligned locking openings 17 which constitute part of the position lock mechanism 5, as will become apparent hereinafter. A bottom surface of the fixed rail 3 is denoted by numeral 7.
The movable rail 4 has a reversed T-shaped cross section and has a vertical wall portion 6 received in the slit 2 and two lower flanges 10a and 10b received in the fixed rail 3. As shown, the movable rail 4 is constructed of two metal plates which are combined in a back-to-back connecting manner. The movable rail 4 comprises the vertical wall portion 6 whose upper end is secured to a seat (not shown) and the two lower flanges 10a and 10b which extend in laterally opposite directions and have leading end portions 19a and 19b bent upward.
As is seen from FIGS. 15, 16 and 17, one of the lower flanges 10a and 10b of the movable rail 4, that is, the flange 10b, is formed with three aligned locking openings 18 each extending to the upwardly bent portion 19b. As is understood from FIG. 15, the lower flange 10b in which the locking openings 18 are formed is the flange which is directed toward the side wall of the fixed rail 3 where the aligned locking openings 17 are formed. The three locking openings 18 constitute part of the position lock mechanism 5, as will become apparent hereinafter.
As may be understood from FIG. 15, rollers (not shown) are disposed on the bottom surface 7 of the fixed rail 3, which rotatably support the two lower flanges 10a and 10b of the movable rail 4, and balls (not shown) are rotatably disposed in two chamber structures each being defined by one inward upper flange 8a or 8b of the fixed rail 3 and one lower flange 10a or 10b of the movable rail 4. With these rollers and balls, the sliding movement of the movable rail 4 relative to the fixed rail 3 is smoothly carried out.
The position lock mechanism 5 comprises a holder plate 12 which is welded to the vertical wall portion 6 of the movable rail 4. The holder plate 12 has a curled supporting portion 13 by which a control rod 14 is rotatably supported. A latch plate 15 having three pawls 16 is secured to the control rod 14 to rotate or pivot therewith.
As is understood from FIG. 15, when the movable rail 4 is slid to a position where the three locking openings 18 of the movable rail 4 are registered with three of the locking openings 17 of the fixed rail 3, the three pawls 16 of the latch plate 15 can enter the registered three pairs of locking openings 17 and 18 to achieve locking between the movable and fixed rails 4 and 3. That is, under this condition, the movable rail 4 is locked at the position relative to the fixed rail 3. Although not shown in the drawings, a biasing spring is incorporated with the control rod 14 to bias the same in a locking direction, that is, in a direction to bias the three pawls 16 of the latch plate 15 toward the locking openings 17 and 18. Thus, when the movable rail 4 is slid to such a registered position, the three pawls 16 of the latch plate 15 are automatically led into the three pairs of the locking openings 17 and 18 to achieve the locking of the movable rail 4.
In this locked condition, the pawls 16 of the latch plate 15 are engaged with not only the locking openings 17 of the fixed rail 3 but also the locking openings 18 of the movable rail 4, and thus a so-called center impelling supporting is effected by each pawl 16. Accordingly, much assured locking is obtained as compared with a locking of a type wherein the pawls 16 are engaged with only the locking openings 17 of the fixed rail 3.
However, the above-mentioned seat slide device 1 has the following drawback due to inherent construction of the lower flange 10b of the movable rail 4.
That is, as is understood from FIGS. 14 and 16, the upwardly bent portion 19b of the lower flange 10b of the movable rail 4 fails to have a robust structure due to provision of the three locking openings 18. More specifically, an apertured part 20 of the upwardly bent portion 19b where the three locking openings 18 are formed fails to have a robust structure. In fact, each locking opening 18 extends close to the top of the upwardly bent portion 19b, which reduces the effective thickness "H" of the portion 19b. Thus, when, due to a vehicle collision or the like, a great force is suddenly applied to the upwardly bent portion 19b through the three pawls 16 of the latch plate 15, such bent portion 19b tends to be severely deformed affecting the center impelling supporting by the pawls 16 by a certain degree. Although usage of a thicker or high rigidity metal plate as a material of the movable rail 4 can eliminate such drawback, weight and cost of the seat slide device are inevitably increased.